Method and apparatus for inductively heating and quench hardening an elongated workpiece

ABSTRACT

A device for inductively heating and quench hardening an elongated workpiece including a heating station having singleturn inductor extending the length of the workpiece for heating the total workpiece simultaneously and as it is rotated; a quenching station having an elongated quench body for quenching the total workpiece simultaneously and as it is rotated; a movable member at the quenching station for bending the workpiece from one side while the workpiece is being rotated whereby the various portions of the workpiece are alternately flexed between compression and tension; and, means for gradually retracting the member from the workpiece so that the amplitude of flexing is decreased until this amplitude is zero. In this manner, the workpiece is straightened as it is quench hardened.

United States Patent Armstrong 51 May 16, 1972 [54] METHOD AND APPARATUS FOR INDUCTIVELY HEATING AND QUENCH HARDENING AN ELONGATED WORKPIECE [52] U.S.C1 ..266/4 E, l48/13l,2l9/10.69 [51] Int. Cl. ..C2ld l/66 [58] Field ofSeareh ..148/143, 144, 153, 154, 155,

148/131; 266/2 R, 4 R, 4 E, 6 R, 6 PC; 219/1065, 10.67, 10.73, 10.69

[56] References Cited UNlTED STATES PATENTS 2,293,534 8/1942 Denneen et al. ..266/4 E 2,504,198 4/1950 Jagen ..266/4E Primary E.taminer--Gerald A. Dost Attorney-Meyer, Tilberry and Body [5 7] ABSTRACT A device for inductively heating and quench hardening an elongated workpiece including a heating station having singleturn inductor extending the length of the workpiece for heating the total workpiece simultaneously and as it is rotated; a quenching station having an elongated quench body for quenching the total workpiece simultaneously and as it is rotated; a movable member at the quenching station for bending the workpiece from one side while the workpiece is being rotated whereby the various portions of the workpiece are alternately flexed between compression and tension; and, means for gradually retracting the member from the workpiece so that the amplitude of flexing is decreased until this amplitude is zero. In this manner, the workpiece is straightened as it is quench hardened.

6 Claims, 7 Drawing Figures SHEET 1 [1F 3 r 2 lm LL H qu m N ll 2 m o l R l H o 2 INVENTOR.

ROBERT G. ARMSTRONG ATTORNEYS PATENTEDHAY 16 1912 3.662 995 sum 2 or a INVENTOR. Fl 2 ROBERT, G. ARMSTRONG ATTORNEYS PATENTEDIAY 16 I972 3. 662 995 sum 3 M3 rrm. I I r m. 1/ 4 i? in |T |J I I64 I60 2 f I: I L// I76 /|62 l r r m L w a QM I48 '46 Q I72 72 FIG. 5

v INVENTOR. I74 ROBERT G. ARMSTRONG ATTORNEYS METHOD AND APPARATUS FOR INDUCTIVELY HEATING AND QUENCII HARDENING AN ELONGATED WORKPIECE This invention relates to the art of induction heating and more particularly to a method and apparatus for inductively heating and quench hardening an elongated workpiece.

The invention is particularly applicable for inductively heating and quench hardening axle shafts having a flange on one end thereof, and it will be described with reference thereto; however, it will be appreciated that the invention has much broader applications and may be used for inductively heating and quench hardening a variety of elongated workpieces.

It has become somewhat common practice to harden the outer surface of axle shafts by inductively heating the surface to a temperature above the critical temperature of the metal forming the axle shaft and then quench hardening the shaft. A variety of apparatus and methods have been developed for accomplishing this function; however, the most commonly used system includes rotating the axle shaft about a vertical axis and progressively moving an energized, encircling inductor along the shaft. A quenching unit directly below the inductor quenches the shaft immediately after it is heated. This type of apparatus was extensively used in hardening axle shafts for the automotive industry. It has been recently suggested that an increased production for the hardening apparatus could be provided by inductively heating the complete length of an axle shaft simultaneously with a single inductor having two conductors extending the length of the shaft. By using this type of apparatus, the quenching arrangement previously used is not appropriate. Consequently, it has been suggested to use a quenching body extending the complete length of the shaft for spraying a quenching liquid against the previously heated shaft, as it is being rotated. Extensive work is being done in developing and improving this type of heating and quenching apparatus.

It has been found that an apparatus for heating and quenching the complete length of an axle shaft in single heating and quenching operations, accomplished over the complete length ofthe shaft simultaneously, may produce an excessive amount of run-out. The present invention is directed toward a quenching device for this type of apparatus which prevents excessive shaft run-out and toward the method performed by this quenching device.

In accordance with the present invention, there is provided a quenching device for quench hardening an inductively heated, elongated workpiece, having a longitudinal axis extending along its length. This device comprises means for rotating the workpiece about the axis, means for spraying a quenching fluid against the workpiece over substantially its complete length, a stressing member, means for moving the stressing member against the workpiece in a direction generally perpendicular to the axis and to a position bending the rotating workpiece into a concave configuration in this direction, and means for gradually withdrawing the member from the afore-mentioned position and away from the workpiece while the workpiece is being rotated and quenched. By utilizing this apparatus, the quenching operation of the device, which is especially adapted for' an apparatus wherein the heating operation is performed by a single turn inductor extending along the total length of the workpiece, minimizes the resulting run-out of the shaft being quench hardened.

In accordance with another aspect of the present invention, there is provided a method of quenching an elongated heated workpiece having a longitudinal axis. This method comprises the steps of spraying a quenching liquid over the length of the workpiece; simultaneously with the spraying step, periodically and repeatedly stressing substantially all portions of the workpiece between a state of compression and a state of tension by rotating the workpiece about the axis with respect to its physical restraint, the position of which determines the flexing amplitude, and gradually decreasing the flexing amplitude by moving the restraint with respect to the workpiece until the amplitude is substantially zero.

The primary object of the present invention is the provision of a method and apparatus for hardening an elongated workpiece, which method and apparatus straightens the workpiece during quench hardening.

Another object of the present invention is the provision of a method and apparatus for hardening an elongated workpiece, which method and apparatus combine a straightening operation with a quench hardening process.

Yet another object of the present invention is the provision of a method and apparatus of hardening an elongated work piece, which method. and apparatus uses a coil to inductively heat the total workpiece whilethe coil is stationary, a quench body for quenching the total workpiece while the body is stationary, and a movable stressing member for transversely flexing the workpiece with gradual decreasing amplitude for straightening the workpiece.

These andother objects and advantages will become apparent from the following description taken together with the accompanying drawings, in which:

FIG. 1 is a side elevational view showing, somewhat schematically, an apparatusutilizing the present invention;

FIG. 2 is a cross-sectional view taken generally along line 2-2 of FIG. 1;

FIG. 2a is anenlarged view showing a certain aspect of the apparatus illustrated in FIGS. 1 and 2;

FIG. 2b is a schematic view illustrating a slight modification of the apparatus illustrated in FIGS. 1 and 2;

FIG. 3 is an enlarged view taken generally along line 3-3 of FIG. 2;

FIG. Us a cross-sectional view taken generally along line 44 of FIG. 3; and,

FIG. 5 is a partial cross-sectional view taken generally along line 5-5 ofFIG. 4.

Referring now to the drawings, wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, FIGS. I and 2 show an apparatus A for inductively heating and then quench hardeningelongated workpieces B, illustrated as axle shafts each having a generally cylindrical body portion 10 and a flange I2 adjacent one end thereof. In accordance with the illustrated embodiment of the invention and as best shown in FIG. 2, apparatus A includes a four station turret 20 which can be indexed between a loading station 22, aheating station 24, a quench hardening station 26 and an unloading station 28. After a workpiece B is loaded onto the turret 20 at loading device 22, turret 20 is indexed to bring the workpiece to the induction heating station 24. At this station, the workpiece is inductively heated, and it is then indexed to the quench hardening station 26 where the workpiece is hardened and straightened in accordance with the present invention. Thereafter, the workpiece is indexed by the turret 20 to the unloading station 28 where it is removed and deposited onto a chain conveyor 30 for movement from the apparatus A.

Referring now to the turret 20, a variety of structures could be utilized for moving the workpiece from station-to-station; however, in accordance with the illustrated embodiment of the invention, turret 20 includesa center shaft 40 indexed by an indexing mechanism 42 which includes a drive motor 44 and an indexing gear box 46. The axle shafts B are supported by the turret in a manner so that they may be rotated. A variety of structures could be used to accomplish this purpose; however, in the illustrated embodiment, stationary abutments 50 are provided with either an upper V-shaped support structure or a set of rollers, as shown. These abutments, or rests, contact the end of the workpiece opposite flange 12 and are spaced about the turret every Of course, any number of stations could be provided in apparatus A, in which case a corresponding number of abutments or rests 50 could be employed. Adjacent the flange 12, there is provided a rotatably driven flange clamp 60 which is rotated by a mechanism carried by the turret, which mechanism is illustrated as drive motors 62. Clamping fingers 64 on the flange clamp are operated by fluid introduced into an operating cylinder 66 having an input hydraulic line 68 connected through appropriate conduits and valves to a hydraulic inlet supply line 70, which is stationary and employs a swivel connection or coupling (not shown). Fluid pressure introduced through inlet 70 is controlled by appropriate valving, not shown, to selectively operate the particular flange clamp to clamp or release an axle shaft from the turret 20. A center 72 is employed by the flange clamp to locate the workpiece with respect to its axis, and an abutment 74 is used as a reaction member against which the fingers 64 pull the centered flange 12 to lock it onto the rotatable flange clamp.

Referring now to the loading device 22, this device, as illustrated, includes two spaced pivoted arms 80, 82 having upwardly facing nests 84 and movable by an operating cylinder 86 between the phantom line position and the solid line position, as shown in FIG. 2. After a shaft has been located in the solid line position shown in FIG. 2, cylinder or pusher rod 88, shown in FIG. 1, moves the shaft B to the right against the center 72. Thereafter, finger 64 clamps the flange 12 against abutment or abutments 74. The left end of the shaft is positioned adjacent to and overlies abutment 50. Manually adjustable rods or bars 90 are used to locate the arms 80, 82 to accept workpieces having various lengths. The operation of the loading device 22 is quite apparent from the above description. The workpiece is placed into the nests 84, in the phantom line position of FIG. 2. The arms 80, 82 are pivoted to bring the workpiece into alignment with center 72. Thereafter, push rod 88 forces the shaft into the flange clamp and the fingers clamp the flange. There is no assurance that the shaft will contact the rest 50; however, the function of the rest becomes important in other stations of the apparatus A.

After being loaded, the shaft is moved by the turret 20 to the heating station 24, best shown in FIG. 2. A power supply 100 is movable in a vertical direction on guide pins 102 by a cylinder 104. In this manner, an inductor 110 may be moved between the solid line and the phantom line positions shown in FIG. 2. Inductor 110 includes parallel conductors 112, 114 which extend substantially the total length of the cylindrical portion of the workpiece and are connected at their respective ends by arcuate connecting legs or conductors 116, 118. One of the parallel conductors is parted and joined to input leads 120, 122, which are electrically connected with the output of power supply 100. During the heating operation, workpiece B is rotated by the flange clamp 60 upon actuation of motor 62. To assure that the workpiece rotates in a controlled manner and that distorted workpieces will not contact the conductor 110, an arrangement is provided for physically forcing the non-flanged end of axle shaft B against rest 50. A variety of structures could be used for this purpose; however, a schematic representation of one of these structures is illustrated in FIG. 2a. In accordance with this embodiment, abutments 130, 132, which may be V-shaped or have a set of rollers, are supported onto a frame 134 so that abutment 130 contacts the shaft B adjacent rest 50 and abutment 132 contacts the shaft generally at its mid-point. In this manner, the abutments hold shaft B against the rest 50 while it is rotated by the flange clamp 60. The abutments 130 or 132 could be individually operated or spring biased to move separately. They can be connected onto the input lead 120 or to another structure movable with or at the same time as the power supply 100. The abutments also maintain proper minimum spacing between the inductor and the workpiece.

In operation of the heating station 24, the inductor 110 is raised by the power supply 100 before a workpiece is moved into the heating station. Thereafter, the inductor 110 is shifted downwardly to form a magnetic coupling between the conductors and the cylindrical body portion 10. In this position, the power supply is energized and motor 62 rotates the axle shaft.

The abutments 130, 132 maintain the axle shaft in alignment.

The heating is effected simultaneously over the length of the workpiece. In some instances, the conductor cannot be moved solely in a vertical direction because conductor 118 may interfere with the clamping fingers 64 if the conductor is to be spaced closely adjacent flange 12. To overcome this difficulty, it is within the contemplation of the present invention to move the inductor at an angle with respect to the axis of the workpiece. This arrangement is schematically illustrated in FIG. 2b wherein the power supply and the inductor are moved along an angled path a from an up" position to a down" position. Of course, other angled paths could be used to allow close coupling of the inductor 118 with respect to the flange 12 without interference with fingers 64.

The present invention primarily relates to the quench hardening station 26, the structure of which is best illustrated in FIGS. 3-5. In accordance with the preferred embodiment of the present invention, the quench station includes a C-shaped quench body having a longitudinally extending, workpiece clearance opening 142. The length of the quench body generally corresponds with the heated length of the cylindrical body portion 10. The quench body includes an internal liquid passage 146 terminating in a plurality of aperture means or holes 148 through which the quenching liquid is sprayed against a workpiece B as it is rotated by motor 62. A liquid inlet means 150 directs quenching liquid to the internal passage 146. The quench body is secured onto supports 152 which, in turn, are connected to guide rods 154, 156 slidably received within bushings 160, 162. An operating arm 164 powered by a pneumatic or hydraulic cylinder 166 moves the quench body toward and away from the workpiece B.

In operation, the cylinder 166 retracts the quench body 140 before a workpiece is moved into or away from the quench station. With the quench body retracted, a heated workpiece B is indexed by turret 20 to the quench station. Cylinder 166 then shifts the quench body to the position illustrated in FIGS. 3 and 4. By an appropriate control, the heated workpiece is rotated about its axis and liquid is sprayed thereon through holes 148. In this manner, the complete length of the workpiece is quenched hardened simultaneously. In accordance with the invention, during the quench hardening operation, the cylindrical portion is straightened by the mechanism similar to that illustrated in my prior US. Pat. No. 3,2l3,659. This mechanism, as illustrated, includes a workpiece stressing member 170 terminating in spaced rollers 172, 174 and movable in a controlled manner by a drive arrangement, schematically illustrated as a power cylinder 176.

In operation of the straightening mechanism, the member 170 is forced into the rotating workpiece B with a force sufficient to plastically deform the workpiece as it is being quench hardened. In this manner, the actual axis b of the workpiece is forced beyond the neutral or desired axis c of the work iece. As the workpiece is rotated, the various portions of the cylindrical portion 10 are periodically and repeatedly tensioned and compressed by flexing the shaft with stressing member 170. Thereafter, the stressing member 170 is gradually withdrawn from the workpiece. This reduces the flexing amplitude defined by the difference between axes b and c. When the cylindrical portion 10 becomes straight and the actual axis 17 corresponds with the neutral axis 0, further retraction of the stressing member withdraws the stressing member from the workpiece. This leaves the workpiece substantially straightened during the quench hardening operation. N0 subsequent straightening is required. This simultaneous quenching and straightening of the workpiece induces straightening while austenitic field is being transformed to martensite. This provides an improved surface strength for the workpiece.

After shaft B is quench hardened and straightened, the workpiece is indexed to the unloading station 28, best shown in FIG. 2, where spaced arms 180, 182 are pivotally mounted onto the apparatus A and have upwardly facing nests 184. The cylinder 186 shifts the arms 180, 182 between the phantom line position and the solid line position shown in FIG. 2. In the solid line position, the chain conveyor 30 picks off the hardened and straightened shafts by any appropriate mechanism. In accordance with the illustrated embodiment, conveyor 30 includes spaced driven chains 190, 192 including a plurality of spaced pick-up plates or stations 194. The operation of the conveyor 30 is apparent from the drawings and the above description.

For simplicity, the necessary hydraulic and electrical controls are not illustrated. Various arrangements could be utilized for accomplishing the functions which are to be performed by the apparatus A.

Having thus described my invention, I claim:

1. In a device for inductively heating and quench hardening an elongated workpiece having a cylindrical portion with a longitudinal axis, a maximum diameter, and two spaced ends, said device comprising: an induction heating station; a quench hardening station; means for supporting said workpiece at said ends for rotation generally about said axis; and, means for conveying said workpiece from said heating station to said quenching station, the improvement comprising: said-heating station including an elongated inductor having two, generally parallel conductors extending generally parallel to said workpiece axis and covering substantially the complete length of said cylindrical portion, power supply means for energizing said inductor, and means for rotating said workpiece about said axis; and, said quenching station including quenching means extending substantially the complete length of said cylindrical portion for spraying a quenching liquid against said portion, means for rotating said workpiece generally about said axis, a single workpiece stressing member adapted to contact one side of said workpiece, two support means movable with the workpiece and on the opposite side of said workpiece from said stressing member, means for moving said stressing member against said workpiece between said end positioned support means in a direction generally perpendicular to said axis and to a position bending said rotating workpiece into a concave configuration in said direction and means for gradually withdrawing said member from said position and away from said workpiece while said workpiece is being rotated and quenched.

2. In a device for inductively heating and quench hardening an elongated workpiece having a cylindrical portion with a longitudinal axis, a maximum diameter, and two spaced ends, said device comprising: an induction heating station; a quench hardening station; means for supporting said workpiece at said ends for rotation generally about said axis; and, means for conveying said workpiece from said heating station to said quenching station, the improvement comprising: said heating station including an elongated inductor having two, generally parallel conductors extending generally parallel to said workpiece axis and covering substantially the complete length of said cylindrical portion, power supply means for energizing said inductor, and means for rotating said workpiece about said axis; and, said quenching station including quenching means extending substantially the complete length of said cylindrical portion for spraying a quenching liquid against said portion, means for rotating said workpiece generally about said axis, a workpiece stressing member, means for moving said stressing member against said workpiece in a direction generally perpendicular to said axis and to a position bending said rotating workpiece into a concave configuration in said direction and means for gradually withdrawing said member from said position and away from said workpiece while said workpiece is being rotated and quenched, said quenching means includes an elongated C-shaped body having an elongated longitudinally extending opening with a width greater than said maximum diameter and means for moving said body in a direction transverse to said axis and between a first position remote to said workpiece and a second position with said body surrounding said workpiece,

3. The improvement as defined in claim 2 wherein said quench means includes an opening through which said stressing member passes.

4. In a device for inductively heating and quenchhardening an elongated workpiece having a cylindrical portion with a longitudinal axis, a maximum diameter, and two speed ends, said deyice comprising: an induction heating station; a quench hardening station; means for supporting sai workpiece at said ends for rotation generally about said axis; and, means for conveying said workpiece from said heating station to said quenching station, the improvement comprising: said heating station including an elongated inductor having two, generally parallel conductors extending generally parallel to said workpiece axis and covering substantially the complete length of said cylindrical portion, power supply means for energizing said inductor, and means for rotating said workpiece about said axis; and, said quenching station including quenching means extending substantially the complete length of said cylindrical portion for spraying a quenching liquid against said portion, means for rotating said workpiece generally about said axis, a workpiece stressing member, means for moving said stressing member against said workpiece in a direction generally perpendicular to said axis and to a position bending said rotating workpiece into a concave configuration in said direction and means for gradually withdrawing said member from said position and away from said workpiece while said workpiece is being rotated and quenched, said supporting means including a rotatable clamping mechanism at one end of said cylindrical portion and an abutment at the other end, and said heating station includes means for forcing said workpiece against said abutment while said workpiece is being heated and rotated.

5. The improvement as defined in claim 4 wherein said stressing member contacts said workpiece on a side of said workpiece opposite to said abutment.

6. In a device for inductively heating and quench hardening an elongated workpiece having a cylindrical portion with a longitudinal axis, a maximum diameter, and two spaced ends, said device comprising: an induction heating station; a quench hardening station; means for supporting said workpiece at said ends for rotation generally about said axis; and, means for conveying said workpiece from said heating station to said quenching station, the improvement comprising: said heating station including an elongated inductor having two, generally parallel conductors extending generally parallel to said workpiece axis and covering substantially the complete length of said cylindrical portion, power supply means for energizing said inductor, and means for rotating said workpiece about said axis; and, said quenching station including quenching means extending substantially the complete length of said cylindrical portion for spraying a quenching liquid against said portion, means for rotating said workpiece generally about said axis, a workpiece stressing member, means for moving said stressing member against said workpiece in a direction generally perpendicular to said axis and to a position bending said rotating workpiece into a concave configuration in said direction and means for gradually withdrawing said member from said position and away from said workpiece while said workpiece is being rotated and quenched, means for shifting said inductor between a first position remote from said workpiece and a second position adjacent said workpiece cylindrical body, said workpiece having a flange at one of said ends and said shifting means including means for guiding said inductor in an angular path with respect to said cylindrical portion with said first position being farther from said flange than said second position. 

1. In a device for inductively heating and quench hardening an elongated workpiece having a cylindrical portion with a longitudinal axis, a maximum diameter, and two spaced ends, said device comprising: an induction heating station; a quench hardening station; means for supporting said workpiece at said ends for rotation generally about said axis; and, means for conveying said workpiece from said heating station to said quenching station, the improvement comprising: said heating station including an elongated inductor having two, generally parallel conductors extending generally parallel to said workpiece axis and covering substantially the complete length of said cylindrical portion, power supply means for energizing said inductor, and means for rotating said workpiece about said axis; and, said quenching station including quenching means extending substantially the complete length of said cylindrical portion for spraying a quenching liquid against said portion, means for rotating said workpiece generally about said axis, a single workpiece stressing member adapted to contAct one side of said workpiece, two support means movable with the workpiece and on the opposite side of said workpiece from said stressing member, means for moving said stressing member against said workpiece between said end positioned support means in a direction generally perpendicular to said axis and to a position bending said rotating workpiece into a concave configuration in said direction and means for gradually withdrawing said member from said position and away from said workpiece while said workpiece is being rotated and quenched.
 2. In a device for inductively heating and quench hardening an elongated workpiece having a cylindrical portion with a longitudinal axis, a maximum diameter, and two spaced ends, said device comprising: an induction heating station; a quench hardening station; means for supporting said workpiece at said ends for rotation generally about said axis; and, means for conveying said workpiece from said heating station to said quenching station, the improvement comprising: said heating station including an elongated inductor having two, generally parallel conductors extending generally parallel to said workpiece axis and covering substantially the complete length of said cylindrical portion, power supply means for energizing said inductor, and means for rotating said workpiece about said axis; and, said quenching station including quenching means extending substantially the complete length of said cylindrical portion for spraying a quenching liquid against said portion, means for rotating said workpiece generally about said axis, a workpiece stressing member, means for moving said stressing member against said workpiece in a direction generally perpendicular to said axis and to a position bending said rotating workpiece into a concave configuration in said direction and means for gradually withdrawing said member from said position and away from said workpiece while said workpiece is being rotated and quenched, said quenching means includes an elongated C-shaped body having an elongated longitudinally extending opening with a width greater than said maximum diameter and means for moving said body in a direction transverse to said axis and between a first position remote to said workpiece and a second position with said body surrounding said workpiece.
 3. The improvement as defined in claim 2 wherein said quench means includes an opening through which said stressing member passes.
 4. In a device for inductively heating and quench hardening an elongated workpiece having a cylindrical portion with a longitudinal axis, a maximum diameter, and two speed ends, said device comprising: an induction heating station; a quench hardening station; means for supporting said workpiece at said ends for rotation generally about said axis; and, means for conveying said workpiece from said heating station to said quenching station, the improvement comprising: said heating station including an elongated inductor having two, generally parallel conductors extending generally parallel to said workpiece axis and covering substantially the complete length of said cylindrical portion, power supply means for energizing said inductor, and means for rotating said workpiece about said axis; and, said quenching station including quenching means extending substantially the complete length of said cylindrical portion for spraying a quenching liquid against said portion, means for rotating said workpiece generally about said axis, a workpiece stressing member, means for moving said stressing member against said workpiece in a direction generally perpendicular to said axis and to a position bending said rotating workpiece into a concave configuration in said direction and means for gradually withdrawing said member from said position and away from said workpiece while said workpiece is being rotated and quenched, said supporting means including a rotatable clamping mechanism at one end of said cylindrical portion and an abutment at the other end, and said heating station inCludes means for forcing said workpiece against said abutment while said workpiece is being heated and rotated.
 5. The improvement as defined in claim 4 wherein said stressing member contacts said workpiece on a side of said workpiece opposite to said abutment.
 6. In a device for inductively heating and quench hardening an elongated workpiece having a cylindrical portion with a longitudinal axis, a maximum diameter, and two spaced ends, said device comprising: an induction heating station; a quench hardening station; means for supporting said workpiece at said ends for rotation generally about said axis; and, means for conveying said workpiece from said heating station to said quenching station, the improvement comprising: said heating station including an elongated inductor having two, generally parallel conductors extending generally parallel to said workpiece axis and covering substantially the complete length of said cylindrical portion, power supply means for energizing said inductor, and means for rotating said workpiece about said axis; and, said quenching station including quenching means extending substantially the complete length of said cylindrical portion for spraying a quenching liquid against said portion, means for rotating said workpiece generally about said axis, a workpiece stressing member, means for moving said stressing member against said workpiece in a direction generally perpendicular to said axis and to a position bending said rotating workpiece into a concave configuration in said direction and means for gradually withdrawing said member from said position and away from said workpiece while said workpiece is being rotated and quenched, means for shifting said inductor between a first position remote from said workpiece and a second position adjacent said workpiece cylindrical body, said workpiece having a flange at one of said ends and said shifting means including means for guiding said inductor in an angular path with respect to said cylindrical portion with said first position being farther from said flange than said second position. 